For several decades it has been known that stellar bars in disc galaxies can be triggered by interactions , or by internal processes such as dynamical instabilities .
In this work , we explore the differences between these two mechanisms using numerical simulations .
We perform two groups of simulations based on isolated galaxies , one group in which a bar develops naturally , and another group in which the bar could not develop in isolation .
The rest of the simulations recreate 1:1 coplanar fly-by interactions computed with the impulse approximation .
The orbits we use for the interactions represent the fly-bys in groups or clusters of different masses accordingly to the velocity of the encounter .
In the analysis we focus on bars ’ amplitude , size , pattern speed and their rotation parameter , { \cal R } = R _ { CR } / R _ { bar } .
The latter is used to define fast ( { \cal R } < 1.4 ) and slow rotation ( { \cal R } > 1.4 ) .
Compared with equivalent isolated galaxies we find that bars affected or triggered by interactions : ( i ) remain in the slow regime for longer ; ( ii ) are more boxy in face-on views ; ( iii ) they host kinematically hotter discs .
Within this set of simulations we do not see strong differences between retrograde or prograde fly-bys .
We also show that slow interactions can trigger bar formation .